Pharmacology
Gastrointestinal
You wish to prescribe an antimuscarinic drug to your patient. Which of the following is a contraindication:
Answer:
Antimuscarinics are contraindicated in:- gastrointestinal obstruction
- intestinal atony
- myasthenia gravis
- paralytic ileus
- prostatic enlargement
- pyloric stenosis
- severe ulcerative colitis
- significant bladder outflow obstruction
- toxic megacolon
- urinary retention
Antimuscarinics
Pharmacology / Gastrointestinal
Last Updated: 15th May 2019
Indications
Antimuscarinics reduce intestinal motility (by acting on acetylcholine receptors and relaxing smooth muscle) and can be used as antispasmodics for the management of irritable bowel syndrome. Hyoscine butylbromide is advocated as a gastrointestinal antispasmodic, but it is poorly absorbed and thus has limited clinical utility.
Other indications for antimuscarinic drugs include arrhythmias, asthma and airways disease, motion sickness, parkinsonism, urinary incontinence, to cause mydriasis and cycloplegia, premedication, and as an antidote to organophosphate poisoning.
Cautions
Antimuscarinics should be used with caution in:
- acute myocardial infarction
- arrhythmias (may be worsened)
- autonomic neuropathy
- cardiac insufficiency (due to association with tachycardia)
- cardiac surgery (due to association with tachycardia)
- children (increased risk of side effects)
- conditions characterised by tachycardia
- congestive heart failure (may be worsened)
- coronary artery disease (may be worsened)
- diarrhoea
- elderly (especially if frail)
- gastro-oesophageal reflux disease
- hiatus hernia with reflux oesophagitis
- hypertension
- hyperthyroidism (due to association with tachycardia)
- individuals susceptible to angle-closure glaucoma
- prostatic hyperplasia
- pyrexia
- ulcerative colitis
Contraindications
Antimuscarinics are contraindicated in:
- gastrointestinal obstruction
- intestinal atony
- myasthenia gravis
- paralytic ileus
- prostatic enlargement
- pyloric stenosis
- severe ulcerative colitis
- significant bladder outflow obstruction
- toxic megacolon
- urinary retention
Side Effects
Many drugs have antimuscarinic effects; concomitant use of two or more such drugs can increase side effects such as dry mouth, urine retention, and constipation.
Side effects of antimuscarinics include:
- dilation of pupils with loss of accommodation (cycloplegia) and photophobia resulting in blurred vision ("Blind as a bat")
- dry mouth, eyes and skin ("Dry as a bone")
- elevated temperature ("Hot as a hare")
- skin flushing ("Red as a beet")
- confusion or agitation particularly in the elderly ("Mad as a hatter")
- reduced bronchial secretions
- transient bradycardia followed by tachycardia, palpitation and arrhythmias
- urinary retention
- constipation
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
